Methods for manufacturing a silicon single crystal include a CZ (Czochralski) method, in which high-purity polysilicon is melted in a quartz crucible and is brought into contact with a seed crystal followed by slow growing and pulling; and an FZ (Float Zone) method, in which a single crystal is obtained by heating a part of rod-shaped high-purity polysilicon to form a melting part between the rod-shaped raw material crystal (polysilicon, etc.) and a single crystal positioned below to become a seed crystal, followed by moving the whole body downward while the melting part is supported by surface tension, and cooling the melting part.
Silicon single crystals manufactured by the CZ method is contaminated with oxygen from a quartz crucible. When the concentration thereof is high, many nuclei of oxygen defects are contained. On the other hand, silicon crystals manufactured by the FZ method described above, having low oxygen content, contain few nuclei of oxygen defects.
Patent Document 1 discloses manufacturing an FZ silicon single crystal by an FZ method using a CZ silicon single crystal produced by a CZ method as a raw material rod. Patent Document 1 also discloses that thus manufactured FZ silicon single crystal has low oxygen content too.
It is known that a p-type silicon substrate doped with gallium is used as a silicon substrate for a solar cell in order to prevent decrease in the minority carrier lifetime (e.g., see Patent Document 2).